Connecting sites using BBMDs

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Connecting Two (or more) Remote Sites Using BACnet

A not-so-tongue-in-cheek review of what is required to hook together two BACnet Sites.

1. Read and enjoy BACnet Specification Addendum O

2. Purchase two devices that have BBMD functionality

2.1. Configure BBMD device according to Manufacturer's instructions

2.2. Determine if the site uses DHCP or Static IP, or Hybrid addressing schemes.

2.3. If the site uses DHCP only you are SOL.

2.4. If the site uses Static IP addressing, obtain an IP address from the IT department.

2.5. If the site uses Hybrid addressing (a combination of a dynamic block of IP addresses and a statically assigned block of IP addresses), obtain an IP address from the static block of IP addresses.

2.6. Configure the BBMD device with the assigned IP address. We will call this IP-B for this site.

2.7. Obtain the Inside IP address and password for the firewall/NAT router at the perimeter of this site. We will refer to the inside IP address as IP-C.

2.8. Obtain the Outside IP address for the firewall/NAT router at the perimeter of this site. We will refer to this IP address as IP-A.

2.9. Ensure that this IP address (IP-A) is a static IP address. You need to contact and arrange this with your ISP. Normally there is an additional charge for this service. These IP addresses are becoming RARE. Bear in mind that since you want to link two sites together you will eventually need 2 of these (actually one for each site you eventually join together). These prices range up to $40 per month. Easily.

2.10. Arrange that the firewall/NAT device at the internet perimeter of the site has an available port (usually port 47808) but it could be another available port. It is important to remember this port number for later in this process. We will call this PORT-A for this site.

2.11. Configure the firewall/NAT device so that incoming UDP packets (from the Internet to the site) that are addressed to PORT-A are forwarded to IP address IP-B.

3. Congratulations, you are almost halfway there.

4. Repeat steps 2.1 to 2.11 for each site. Making notes of the IP addresses and ports used as you go along.

4.1. Now revisit each BBMD and configure the BBMD table, per manufacturers instructions, with the IP addresses of the peer devices at the other sites. You have to enter the Outside IP address (IP-A) in this table, since the actual IP address of the BBMD (IP-B) is hidden behind the NAT router.

5. Repeat step 4.1 for each site.

6. Test this configuration by sending a Who-Is from Site A and confirming that you can see all the devices at the other site(s).

7. Debug.